Pattern elimination for molds



Feb. 7, 1928.

A. HUDSON PATTERN ELIMINATION FOR MOLDS 2 sheets-sheet 2 Filed June 25. 1925 5. R V1 F M m hm W Y n b w M w H, MS Il www@ W GIN. l hM. I. -w mw @b n ,Nml ON l N w d A IIL. D. f Il mi W\ n M W\ b` QW `Patented Feb. 7, 1928.

UNITEDv STATES PATENT omer..

ALDEN HUDSON, 0F GREEN BAY, WISCONSIN.

PATTERN ELIMINATION FOR MOLDS.

Application iled June 25,

tern materials from larly intended for use` as a piece to facilitate the-removal of wax machinery a mold. It is particuof dental from a mold made for the casting of a gold inlay or the like.

It has quite generally been the practice to eliminate the wax from a mold'by heating 1l) the mold or investment and allowing the wax to be taken up'by the porous mold. Plaster of Paris with other plastic materials is the ordinary material employed for the making of the mold, but Where plaster of Paris is used the heat must be applied with great oare'lest any excess of moisture in the 'plaster of Paris should be turned so rapidly into steam that it could not escape but by bursting or cracking the mold. A

further objection experienced heretofore in the use of plaster of Paris has consisted in the fact that when the wax is the porous body of the is apt to penetrate heated a portion of it mold and remain therein. Where this occurs a defective casting results.

' In order to overcome these cial investment mate diiiiculties sperials have been devised which will stand the sudden application of high temperatures without cracking, and which are sutliciently non-porous topreventabsorption of Wax from the pattern. special materials, however,

pensive and diicult Such are not only exto procure, but are unf necessary in ylieu of the -apparatus and method hereinafter to be described.

. It is the object of this invention to provide a simple and inexpensive mechanism for the removal of pattern material from any mold without necessitating the application of excessive heat, l

portions of the pattern ger of permitting material to penetrate the mold. More particularly stated,

of this invention to subject a mold attern simultaneously to heat and to obj ect and and without anyv danporous body of the it is the centrifugal force acting in a direction to expel the pattern material from the moutlr of the mold. It is a further object of the V4invention to provide for the rotation ofthe mold during' the above mentioned operation to ensure against the contributing of any of the pattern material in any corner of the mold which would otherwise be obscure and tend to retain such material therein.

In the drawings: Figure 1 is a si de elevation, partially.

1925. Serial No. 39,443.

broken away to a vertical axial section, and illustrating an electrically heated and operated device embodying this invention.

Figure 2 is a detail view in end elevation on a reduced scale of a part of the oven shown in Figure 1.

Figure 3 is a side elevation, partially broken away to a vertical axial section, and illustrating a gas heated and electrically operated device embodying this invention.

'Like parts are identified by the' saine reference characters throughout the several views.

The base 5 supports a gear housing 6 and a motor 7. The armature tor extends into the gear housing and carries afpinion 9 meshing with a gear 10 on the vertical shaft v11 'of the device.

"A-boss 12 extending upwardly above the gear housing in the form of a vertical sleeve integrally connected therewith provides a convenient A means for mounting suitable bearings 13 and 14. for shaft 11.

The upper end of shaft 11 is threaded to receive a nut 15 and secures thereto the' fitting 16 from which the shaft arms 17 and 18 extend transversely in a substantially horizontal plane. These shaft arms are in alignment and may conveniently be constructed integrally with. fitting 16. A rotary sleeve 19 is carried by suitable bearings 20 and 21 from shaft arm 17 and is flanged at 22 for the support of a rotary oven designated in its entirety by reference character 23. y

Thegoven proper comprisesy a cup-like shell 24 shouldered at 25 to fit within thel end of sleeve 1.9. Concentric with this shell is an annulus 26 secured thereto by means of an annular head 27 and clamped against the shell and the annulus by means of bolts 28,

the oven proper comprising the shell 24.

This shell has a removable cover 35 formed with a.recess or pocket 36 which communicates through opening 37'with the interior shaft 8 of the moy,

resistance coils when a curin correspondin of the oven. Ears 38 on the cover are receivable beneath'lugs 39 on the head or end plate 27 of the rotary oven device. The arrangement is such that 'the door 35 of the oven is readily secured or removed by partially rotating it to engage or disengage the ears 38 beneath the relatively fixed lugs 39 of the head 27. lVhen ,a mold 40 is positioned within the oven and subjected to such heat as to melt the wax pattern 41 therein, the molten material will be expelled centrifugally through the opening 42 in the mold and will enter the recess or pocket 36 in the cover 35 from which it may readily be withdrawn when the cover is removed. The cover thus forms a convenient receptacle for collecting wax or other pattern material expelled from the mold in the use of,

this device and method.

In order to "balance centrifugal pressures developed during the rotation vof the oven about the vertical axis of shaft 11 I preferably provide upon shaft arm 18 a counterbalance 44 -which is positioned thereon by means of nuts 45 and 46 and maybe adjusted axially thereof, as desired.

The rotary sleeve 19 which carries the oven is provided with a flange 47 adjacent its inner. end. An annulus 48 of dielectric material is tted within this flange and 'carries two annular contact rings 49 and 50 of electrically conductive material. Terminals 51 and 52 arefconnected respectively with rings 49 and 50 and are suitably insulated from each other and from flange 47. Conductors 53 and 54 connect termlnals 51 and 52 with terminalsv 33 and 32 upon theexterior of the oven to transmit current from the rings to these last mentioned terminals.

The annulus 55 is guided for axial movement upon the boss or sleeve 12 and is supported by' means of a plurality of springs 56 seated in pockets therein, and also seated pockets in a collar 57 which is adjusta ly positioned by means of set screws '58 on the sleeve 12. The annulus 55 has an annular core of dielectric mate- -rial 59 formed in its upper surface,'and

within this core are embedded annular metallie, tracks 60 and 61. 'Terminals 62 and 63 are insulated from each other and from the annulus 55 but are electrically connected, respectively, with the metallic tracks 210 and 61. -These terminals are supplied wi 1 .current preferably from thev same source which supplies the motor 7 by means of wires 64 and 65. The wheels or disks 49 and l 50 operate respectively upon tracks 60 andA 61 during the rotation of the device about the axis of shaft 11. Thereby the resistance coils 31 are supplied with current from wires 64 and 65 and at the same time the sleeve 19 and the oven sup orted therefrom-are caused to rotate rapi ly upon the horizontal axis of shaft arm 17 during the bodily rotation of the oven and shaft arm about the axis of shaft 11. By way of equalizing the load on shaft 11, II preferably provide an idler wheel 66 which may run directly upon the margin of the annulus 55,

that thel contact surfaces betweenA these wheelsand their respective tracks willv be4 kept clean and free of corrosion. The drive to the shaft 11 for the bodily rotation of the oven and shaft arm 17 about a vertical axis is positive. The drive to the sleeve 19 which rotates the oven on its own axis is frictional and depends solely upon the frictional engagement of `disks 49 and 50 with their respective tracks. The friction between these parts is obviously dependent upon the degree of pressure exerted by springs 56, and such pressure may readily loey controlled by adjusting the collar 57 vertically on sleeve 12. Preferably the degree of vsupport provided through springs 56 will be just suliicient to carry the weight of the oven and counter-balance and related parts without subjecting shaft 11 to any material degree of end thrust. This degrec of pressure is entirely adequate to furnish the requisite friction for rotating the oven on its own axis.

The construction illustrated in Figure3 is similar to that shown in Figures 1 and 2 with the exception that the oven is heated by gas instead of electricity. In this con-- struction thellange 47 itself may be used as the wheel which frictionally imparts to the oven rotation upon its own axis. It is unnecessary to use the metallic disks 49 and 50 since no current is conducted to the oven. The heat-which it is desirable to supply to the oven at all times during the operation of the device is furnished bymeans of a large annular gas burner 70 which may conveniently be carried by arms 71 from the gear housing 6; The arms 71 have extended portions 72 which support an annular shield 73. The purpose .of the shield is to confine the flame to the oven and to prevent any Wind developed: during the operation of the oven from dlrectngvthe' gas-Hams outwardly. The oven 24 in this device comprises in effect an extension of sleeve 19 which corresponds to sleeve 19 inthe electrically heated device. The sleeve will preferably be provided with ventilation 'apertures at intervals to dissipate excessive heat resulting. from the impossibility of accurately concentrating the heat of a as burner. In both of t ese devices the mold or investcover,

`ment is placed within the oven with its `to the oven either by means of the gas flame shownjm Figure 3 or. by means of the electrical resistance coils shown in Figurerlf It is very. desirable to avoid heating the oven materials before it is in rapid rotation about the vertical axisfof shaft 1'1 and about its own horizontal axis, as represented by shaft arm 17. I have found that when the oven is bodilyvrotated about shaft 11 during the heatingloperation it is not possible to crack the investment 'material whether that material be, plaster of Paris or `any other substance now used for the purpose. I attribute this fact to the powerful centrifugal force which is operating to expel from the mold or investment all material therein which is free to move. including not only the wax but also whether water,'vapor, and steam. It will also'be noted that by reason of the rotation of the oven upon its own axis the thorough expulsion of allmaterial from the mold or investment `is practically assured, even if the orifice 42 opening from the'mold is not in the axialcenter thereof.

All material expelled from the mold is received into recess or pocket 36 of the and when the cover is removed this residue may readily be extracted therefrom,` leaving the interior of theoven clean and in condition for the insertion of another mold or investment. y i.

It is particularly to be noticed that the elements herein designated as ovens are nothf ing more than carriers for the mold or investment. They need not be made liquid tight since the molten pattern material is delivered directly into the recess/in the removable cover. Neither must they be made of the heat insulating material since the heat is at all events applied to the mold which, for the purpose of melting the .pattern, is in the nature of an oven or housing, The sole function oftthe ovenas herein described is`to provide a convenient means df mounting or carrying the mold for its compound rotative movement. Comparative tests lw'tha dental alloy in'- cluding gold and platinum indicate that castings made in investments freed of wax by `this machine are uniformly smaller than the pattern to an extent corresponding to .004 inches shrinkage to one half inch, this being the contraction factor of the metal used. Where the same alloy was used in investments from which wax patterns had been removed by ordinary methods there4 was found to be a variatlon of from .006 to .009 inches to the half inch. This is due to the fact thatiinfordinary methods the wax carbonizes in the investment before it becomes wholly absorbed or fluid. The

burned wax forms a 'fcoating of variable thickness'which results in inaccuracy in the size of the'produet.

A 1. In a device of the character; described,

port and a the combination with a rotary su vrotor mounted on said support orrotation about an axis transverse to the axis of said support, of a track mounted concentrically with the axis of said support and yielldable axially thereof, said track being pressed axially of said support to a position-for 4interaction with said rotor, whereby to impartmovement to said rotor upon the rotation of sai-d support.

2. In a device of the character described, thecombination with a rotary support., of complementary rotors mounted substantially equidistant from the axis of rotation of said support upon opposite sides of said axis, an oven connected with one of said rotors, a track substantially concentric with said axis in contact-with said rotors for the transmission of motion to said rotors upon the rotation of said support, a resistancescoil in operative relation to said oven, and anl electrical connection to sai-d coil including oneof said rotors and said track.

3. In a device of the character described, the lcombination with a shaft mounted for rotation, of a transverse shaft carried thereby, a rotor co-axial with said 'transverse shaft, an electrical resistance connected with said rotor to receive rotation therefrom, a track of electrically conductive material substantially concentric with said shaft, and electrical'connections -to said resistance including said track and said rotor, said track being in operative rotor during the rotation of said shaft and 'being adapted to impart rotative movement thereto while in electrical connection therewith. 4. In a device of the character described, the combination with an electric oven including a heating element and mounted for compound rotation about a plurality of axes, of a track concentricwith oneof said axes and including a pair of mutually insulated concentric electrically conducti'verings, a rotor mounted for movement about said track and for rotation about the other of said axes and -connected with said oven to impart rotation thereto on the axis of which said rotor is rotatable, said rotor being provide-d with mutually insulated annular contact surfaces in engagement respectively with the rings of said track and electrically connected with the heating elements of said oven, whereby said rings and said rotor include parts of a circuit for transmitting electrical current to the element of said oven.

5. In a device of the character described, the combination with a rotary support, of complementary rotors mounted on opposite engagement with said i llO sides of said support and adapted for rotation u n an axis transverse with respect. to that o said support, an oven connected with ,one

vof saidgirotors for rotation about said transverse axis, a heating element for said oven, and an electrically conductive ring yieldably pressed axially of said support into engage- Jment with one of said rotors, said last mentioned rotors being provided with an an;4A nular conductive surface traveling about sai-dy ring and in electrical connection with the heatingelement of said oven, and means for equalizing forces acting on said support during the rotation of said oven. v

6. In a device of the character described, the combination" with a rotary support, of a transverse shaft mounted thereon, a rotor rotatable on said shaft on one side 'of said support andl including a carrier for an investment, a second rotor idly rotatable about 4said shait't on the opposite side of said support,ja' relatively stationary bearing for said suppor', an` annulus mounted concentrically of said su portland splined to said bearing, each o said rotors havin portions adapted for travelingvcontact wit said annulus, and aJ spring pressing said annulus along sa1dw, support 1n the direction vof said -rotor portions, whereby to transmit rotative movement'to said rotors during the rotation of said support. v

7. In a device of the characterf described, the combination withA arotary support, of an oven mounted thereon at a 'point remote from said su port andV provided with an aperture opemng radially outwardly, and a remoyable cap for said oven containing a compartment adapted to receive material ejected lconcentric'all'y from said oven;

8. In a device of the character described, the combination' with' a rotary supportand a transverse shaft mounted thereon, of an oven rotatable on said sha-ft at onev side of said support, a counter-Weight on said shaft on 

